For growth modelling with categorical observed variables using THETA parameterization, is it possible to calculate estimated outcome probabilities for chosen values of covariates on the slope factors? How is this achieved?

Not quite, I want to estimate the outcome probability for a chosen value of the covariate, for the mean slope value. So although s is continuous, I want to know the probability of this mean value when the covariate moves from 0 to 1.

The reason I want to do this is because probit coefficients are not very meaningful, due to the scale of the slope growth factor. My model can only be run in THETA mode.